Nato escalated its attacks on Col Muammar Gaddafi by destroying his main office building just hours after it came under political pressure to target the Libyan leader.

Libyan officials were quick to condemn the air strikes on Col Gaddafi's sprawling Bab al-Azizia compound in southern Tripoli as an attempt to "assassinate" their leader.

Two explosions, audible over a mile away, were heard from the compound in the early hours of Monday morning.

Tripoli residents said they were the loudest heard since Nato's air campaign against Col Gaddafi's forces began.

The Libyan leader is not thought to have been at the scene of the blasts, which destroyed a small complex of buildings where he recently hosted delegates from an African Union peace mission.

Libyan officials claimed that 45 people were wounded, 15 of them seriously, in the attack, but did not take Western correspondents to see any of the casualties. "It was an attempt to assassinate Col Gaddafi," one official said.

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Nato said the facilities had been used to co-ordinate attacks against Libyan civilians. "Nato carried out a precision strike in central Tripoli last night," Oana Lungescu, the Nato spokesman, said. "The target was a communications headquarter that was used to co-ordinate attacks against civilians." The organisation warned that it would maintain its offensive until Col Gaddafi's regime no longer posed a threat to Libyan civilians. "We will keep up the pressure until all attacks against civilians have stopped, Gaddafi's forces have withdrawn to bases and full and unimpeded humanitarian access has been ensured," she said.

Three state television stations went off air after the attacks, but normal transmission was restored within an hour.

The attacks came after calls by some US politicians over the weekend to target Col Gaddafi.

Such a course of action has been strongly opposed by Russia and some other states, which have argued that "regime change" runs counter to the UN resolution authorising military action in Libya.

Saif al-Islam, one of Col Gaddafi's sons, said the Nato strikes would not deter the Libyan government in its campaign against the rebels.

"This cowardly attack on Muammar Gaddafi's office may frighten or terrorise children but we will not abandon the battle and we are not afraid," he said.

Another Libyan official said the attack would justify Libyan terrorist action against the cities of Nato members.

Meanwhile, pro-Gaddafi troops shelled residential areas in Misurata, the rebel-held city, with a ferocity that a revolutionary spokesman described as "unprecedented".

Liam Fox, defence secretary, will meet Robert Gates, his US counterpart, in Washington on Tuesday to discuss how the coalition can undermine Col Gaddafi’s regime. Sources said they will discuss “targeting” and cutting fuel supply lines to Gaddafi’s forces.

Dr Fox suggested on Monday that Col Gaddafi was a target. “All parts of command and control are legitimate targets so long as they are attacking civilians,” he said. “Those who are involved need to recognise we regard them as a legitimate target.”